Historically, computer systems comprised "main frame" systems. That is, a "main frame" computer, various interfaces, and user terminals. The term "main frame" means that the computer for the entire system is located or housed in a single box or frame, rather that distributed throughout the system. Accordingly, in the traditional approach, a single computer held responsibility for computational tasks, interface control, driving the monitor on the user terminals, reading the keystrokes of each user keyboard, and maintaining a master data base containing all data files, records, and programs.
In actual use, these system were cost effective only for large operations The main frame computer, being the heart of the system, commanded the major portion of the purchase price, which required small users to buy a more powerful system than was needed. Alternately, the purchase of a "small system" generally resulted in expansion problems when the small user grew to an intermediate size, and was force to purchase yet another computer system. For these reasons, distributed or modular computer systems became the preferred approach in many traditional main frame applications.
In a distributed computer system, the computational power (or intelligence) is distributed throughout the system. To fully exploit the benefits of a distributed system, the fundamental operation of the system must be changed. In addition to distributing the hardware (i.e., computing nodes in place of "dumb" terminals), the data base or software must also be distributed. Thus, each computing node assumes responsibility for maintaining a self-satisfying portion of the entire data base. That is, all data files or records and the operating program required to manipulate and display the data under normal operating conditions reside within the computer node. Normally, the distributed computing nodes are interconnected via some communication network to allow communication of data files or programs between computing nodes. If a computing node requires information supplemental to that of its data base, a request for the required information may be transmitted to the appropriate node via the interconnecting network. In this way, full access to all information is provided in a distributed and readily expandable computer system.
In a basic trunked communication system there exists a high degree of flexibility to partition conversations between different groups so that no one agency or district is aware that another agency or district is using the system. These groups can be subdivided into subgroups, so that only those individuals who need to communicate together on a normal basis are aware when a conversation is in progress. Further, an individual may initiate a private conversation between only two parties without disturbing either the remaining subscribers in the group or subgroup within which that individual normally operates.
A typical example of such a hierarchy may be a group ID assigned to a construction company, and subgroups assigned to management personnel, delivery personnel, and various on-site teams. Of course, each subscribing unit has its own individual ID for individual calls. Thus, all of management personnel may communicate on a subgroup basis without disturbing the other personnel in the construction company. Also, a group-wide call may be made to all individuals associated with the construction company. The same hierarchical analogy can be drawn to the public safety market. For example, the groups could be fire and police departments and the subgroups consisting of individual districts.
The individuals communicating via a trunked communication system are normally referred to as subscriber units. Generally, a subscriber may be a portable unit, mobile unit, or a control station. Typically, a portable unit is designed to be carried on or about the person. A mobile unit is normally designed to be used in vehicles. A control station is usually understood to be a permanent or semi-permanent installation in a building or other fixed location. As used herein, all these communicating units or stations are collectively referred to as subscriber units.
Generally, it is known to use a subscriber's identification (ID) code to effectuate the desired type of communication. Accordingly, each subscriber contains a code plug or a programmable read only memory (PROM) that specifies the group, subgroup, and individual ID's that enable the subscriber to participate in either an individual, subgroup, or group-wide call. If a subscriber unit is programmed to allow communications in more than one subgroup, a selection mechanism, for example, a selection switch, is used by the subscriber to select the particular subgroup in which it desires to operate.
To initiate a call, a subscriber unit transmits a "channel request" inbound signalling word (ISW) to the central controller of the trunked communication system. The central decodes this request and, if a communication channel is available, returns a "channel grant" outbound signalling word (OSW) consisting of the requesting unit's ID code and the identification of the assigned channel. The channel grant causes the requesting subscriber to move to the assigned channel and begin transmitting, while causing the remaining units in the group, subgroup, or an individual (depending upon whether a group, subgroup, or individual call was requested) to move to the assigned channel as listening units. In this way, trunked communication is established.
In particular implementations of trunked communications systems, it is desirable to have one or more dispatchers monitor all calls occurring on the trunked communication system. For example, public safety communications systems are often required by regulatory agencies to provide at least one dispatcher to monitor and control the communication system at all times. Accordingly, some communication systems include a dispatcher console that may initiate or monitor the trunked system. Generally, the dispatcher is given additional powers such as the ability to take over a communication channel during an emergency situation.
In addition to voice messages, predetermined status messages are often used in trunked communication systems to rapidly convey status information of an ordinary nature. For example, "available" or "at scene" may be typical status messages employed by a police or fire department. To transmit these messages, it is known to have a small status panel having numerous activators to automatically send these messages in addition to the identification code of the subscriber reporting status. The dispatcher terminal may illuminate certain indicators to indicate the status of an individual subscriber unit.
However, in a system having a large number of subscribers it often becomes impractical to have the individual status indicators for each subscriber. Moreover, as a subscriber changes groups or subgroups it may be impossible to reconfigure the status indicators to properly inform the dispatcher of the subscribers activities or status. Accordingly, a need exists for an effective status reporting and dispatch system to enable efficient and effective control of the trunked communication system.